Parker Chomerics CHO-FAB CFT shielding tape is a conductive fabric tape built on a ripstop woven polyester carrier metallized with copper and nickel. The conductive path is maintained across the fabric surface and through a conductive pressure-sensitive acrylic adhesive. The product is supplied on a release liner and is used in enclosure seams, cable-shield terminations, and cover edges where a die-cut conductive fabric gasket is not available. Manufacturer-published nominal construction data list a total thickness of 0.10 mm (0.004 in) and standard roll widths of 25.4 mm, 50.8 mm, and 101.6 mm. Surface resistivity determined by ASTM D4496-21 is typically not greater than 0.05 Ω/sq. Because the fabric is woven rather than continuous foil, the measured surface resistance is direction-dependent; the highest resistance may occur across the weft and warp yarn intersections under low contact pressure.

Shielding effectiveness should be specified by test configuration. Plane-wave attenuation measured with a modified IEEE 299 fixture on an aluminum aperture plate is typically reported at ≥ 60 dB from 20 MHz to 10 GHz for a single layer with proper grounding. At lower frequencies the tape is not a magnetic absorber. Magnetic-field shielding below 1 MHz depends on the joint inductance and enclosure geometry rather than the fabric alone. Peel adhesion at 180° to stainless steel under ASTM D3330-04 Method A is frequently used as the incoming-materials control method. The continuous service temperature range is normally stated as -40 °C to 121 °C, with short excursions above 150 °C permitted only for reflow or bake cycles documented by the manufacturer.

How Does a Nickel-Copper Ripstop Fabric Tape Compare with Solid Copper Foil and Aluminum Foil Shielding Products?

In a comparison against solid copper foil tape, CHO-FAB CFT has lower longitudinal conductivity because current flows through a plated woven scrim rather than a continuous foil. Copper foil tape typically shows surface resistivity below 0.01 Ω/sq and higher plane-wave attenuation above 80 dB in the same fixture. The fabric tape compensates with higher tear strength and flex endurance. Solid foil products wrinkle and crack when stretched over curved returns, whereas the ripstop polyester fabric can be formed around a radius below 6 mm without tearing. Aluminum foil tape provides continuous lower surface resistivity, but its galvanic potential is more negative than the nickel-copper fabric when coupled to steel or aluminum. Oxidation of aluminum surfaces can raise contact resistance over time unless the conductive adhesive is applied under sufficient pressure and the joint is protected from moisture.

For cable shield termination, the tape is typically wrapped around a braided or foil cable shield and a metal connector backshell with 50% overlap. The conductive acrylic adhesive provides electrical contact only when the liner is removed cleanly and the tape is burnished with a rigid roller. Joint resistance measured from connector backshell to cable shield with a four-wire milliohm meter should be below 0.05 Ω on first article units. Production lines using automatic tape dispensers require controlled unwind tension because the ripstop carrier can telescope on the roll when the release liner is pulled at high speed.

In enclosure seam applications, the tape is often die-cut into strips rather than applied directly from the roll. Die-cut strips reduce tolerance stack-up in high-volume assembly because the tape width can be matched to the flange land. A pneumatic or manually operated roller conforms the adhesive to the plating topography. Plating thicknesses of 5 μm to 15 μm on steel or aluminum flanges have been sufficient when the chromate conversion coating is sealed and dry. Electrical contact to bare aluminum should be verified for galvanic corrosion risk. Field data from metal enclosure lines show that edge lift is the dominant failure mode when the tape is applied over a powder-coated flange because the adhesive bonds to the powder surface rather than the conductive substrate. If the flange is not masked before powder coat, a separate conductive insert or masked conductive land is required. On electroless nickel-plated flanges, phosphate residues from pretreatment can survive alkaline cleaning and produce a nonconductive boundary layer. A contact-resistance test or four-wire probe should be used after cleaning on a first article basis.

When CHO-FAB CFT Replaces Die-Cut Fabric Gaskets in Flanged Enclosure Seams

Die-cut gaskets impose tooling lead time and require a continuous groove or retaining feature. CHO-FAB CFT can be laminated directly onto a flat flange with no groove, provided the flange width is at least 3 mm and the mating cover applies uniform pressure. The adhesive system is not a foam core and does not provide low closure force or compression set. Therefore, the joint should be designed with continuous metal-to-metal contact along the tape edge to carry current. If the cover is bowed, intermittent contact can produce slot-antenna leakage at frequencies where the seam opening approaches a half wavelength.

Because the acrylic pressure-sensitive adhesive is a polyacrylate system, it should not be specified in continuous contact with plasticized polyvinyl chloride, low molecular weight hydrocarbons, or ketones at elevated temperature. Plasticizer migration softens the adhesive and can cause edge lifting on cable jackets. The tape is not designed for fluid sealing. Pressure differentials across an enclosure seam require a separate elastomer gasket. At relative humidity above 60% RH, reels should be conditioned in sealed packaging to prevent water condensation on the release liner. Application at substrate temperatures below 10 °C is not recommended because the adhesive does not wet surface roughness well enough to maintain stable electrical contact.

Surface preparation is the main factor that changes production yield. Alcohol wiping with 70% isopropyl alcohol is common for removal of light process oils, but high-load stamping lubricants may require methyl ethyl ketone or a hydrocarbon degreaser followed by a clean wipe. Solvent flash-off should be complete before tape placement. Retained solvent at the adhesive-substrate interface reduces peel adhesion and raises joint resistance after temperature cycling. A lint-free poly-cellulose wipe should be used because paper wipes leave sulfate residues that can accelerate corrosion on nickel-plated fabric. Substrate surface energy should exceed 38 dyn/cm. Untreated polyethylene and polypropylene are not recommended without corona or plasma pretreatment.

On high-volume enclosure lines, batch-to-batch variation in release-liner release force can shift die-cutting kiss-cut depth. An incoming inspection fixture run at 300 mm/min peel rate is used to verify release force before die-cutting. Automatic dispensers with uncontrolled brake torque can telescope the roll after partial use. Constant torque clutches or diameter-compensating unwind spindles are specified. Liner fragments left in the die-cut tape cause insulating regions that may not be visible under low magnification.

Galvanic Compatibility and Low-Frequency Shielding Limits of the Nickel-Copper System

Shielding effectiveness below 10 MHz is governed less by the tape surface resistivity than by the geometry of the seam and the inductance of the enclosure. A conductive fabric tape cannot replace magnetic steel or high-permeability shielding for near-field magnetic absorption. The nickel outer layer provides corrosion resistance and a stable contact surface, but the copper-nickel couple can still participate in galvanic corrosion when the tape is terminated on certain magnesium alloys or when the joint is exposed to salt spray. In salt fog testing conducted under IEC 60068-2-52 or equivalent, the edge of the tape and the exposed metal flange should be inspected for white corrosion products. Pass/fail criteria should be established by the end user because laboratory atmosphere and salt concentration vary.

The tape is used in printed circuit board shield partitions when a low-profile conductive surface is needed without through-hole fasteners. Strips are cut to length, placed across the junction between a board-mounted fence and a cover, and rolled with a silicone-covered mandrel. Electrical integrity is checked by a four-wire probe on a sampling basis. For cable harnesses, the tape replaces copper foil wrappers in applications where repeated flexing causes foil cracking. Because the tape is conductive across its face, overlapping wraps must be burnished to avoid insulating air gaps between the first wrap and the overlapping layer. If a solder connection is brought through the tape, the polyester carrier will melt and the nickel-copper plating will wick. Solder terminations are therefore made to a metal terminal or connector body, not directly to the fabric.